A Tifdwarf bermudagrass golf green, for example, is typically established by planting sprigs or stolons that have been harvested from a registered Tifdwarf sod field. The sprigs or stolons are placed over the finish graded green typically in numbers of 20 to 40 bushels per 1,000 square feet and lightly disc harrowed into the sand surface of the green. In an alternative method, the sprigs are spread on the surface of the green which is then topdressed with approximately 3/8 inch layer of sand that is compatible with the existing soil profile of the green and then rolled. In some instances a light layer of sterile mulch is placed over the planting to help keep it moist.
Many grasses, largely warm season hybrid types, are propagated vegetatively in this manner because they are either sterile and do not produce seed or are very poor seed producers in which case it is more economical to propagate a useful grass vegetatively. Even grasses used for sod production, such as the elite Tifdwarf mentioned above, are planted vegetatively for the production of sod.
Sprigs or stolons are harvested from a sod field by running through it a verticutter. A verticutter is a machine that acts much like a dethatcher with swinging steel blades that cut and lift largely stolons, stem, and leaf material to the surface of the sod. This material is then gathered and sold by the "bushel" as sprigs or stolons for planting. Typically one "bushel" of sprigs or stolons consists of the material that is verticut and gathered from approximately one square yard of conventional sod grown on soil. Thus, an acre (4,840 square yards) of sod for sprigging typically yields 4,000 to 5,000 "bushel" of sprigs. The definition or exact measurement of a"bushel" however varies widely throughout the industry.
A recent innovation in the sod industry as described in U.S. Pat. Nos. 4,986,026, 5,177,898 and 5,301,446 has been the growing of grass sods in contrived media over plastic sheeting. Such a technique has several advantages over the production of sods in the conventional manner on soil. The sods grown over plastic can be harvested much more quickly largely because the primary rooting system of the grasses is used to knit the sod; they are often lighter especially compared to a sod grown on mineral soil; and a wide variety of often waste materials such as various composts, varying grades of sand, conifer barks, and many others can replace topsoil as growing medium.
Warm season grasses can also be adapted to production over plastic sheeting, and it has been the search for an effective method of planting vegetative material, rather than seed, on plastic sheeting that has led to the discovery described below.